1. Field of the Invention
The present invention relates to a portable wrist device having a thermoelectric generator, such as a wristwatch or a pager.
2. Description of the Prior Art
For wristwatches, an example of a portable wrist device, electronic wristwatches have now come into the mainstream, using silver oxide batteries, lithium batteries, etc. as a power source.
However, these batteries are expendable commodities and hence need to be replaced regularly, and thus present the problem of the consumption of the limited resources available on earth.
As a substitute, then, research is being carried out on wristwatches incorporating an internal power generation mechanism.
Known power generation methods include, for example, solar cells that convert light energy, mechanical power generation using gravitational energy, and thermal power generation using the Seebeck effect, based on a temperature difference. Of these mechanisms, the solar cell and mechanical power generation have already been put into practical use. On the other hand, thermal power generation has been disclosed in Japanese Patent Application Laid-open No. Sho 55-20483 (refer to FIG. 1), for example. A frame 104 is made from a heat insulating material, and a metallic back cover 5 is fitted on the bottom side while a metallic bezel 103 is furnished on the top side: to hold a crystal 2. A thermoelectric generator 6 is placed on the inside face of the back cover 5, through a heat conducting plate 107 which has spring-like characteristics. The thermal circuit from the other end of the thermoelectric generator 6 is connected to the bezel 103 through a spring 115, an intermediate ring 108, and a dial 12. This way has theoretically been known for a long time.
When a thermal power generation method is employed in a portable wrist device, the temperature difference between the body temperature (high temperature section) transmitted to the portable wrist device through the wrist, and the ambient temperature around the portable wrist device (low temperature section) is used.
To obtain a sufficient temperature difference to generate the required electric energy from a thermoelectric generator, thermal conductivity from the high temperature section to a heat receiving portion on the thermoelectric generator, and from a heat radiating portion on the thermoelectric generator to the low temperature section are important. There has been a problem of how to supply heat from the heat supply source, i.e., the back cover to the radiating portion on the thermoelectric generator, with other sections insulated from the heat.
Especially for a portable wrist device, the case itself is small, so the frame gets warm through heat transfer from the back coverin a normal mode, and there is at most only a 2xc2x0 C. temperature difference between the back cover and the frame. Consequently, it is standard to use an insulating material to insulate between the back cover and the frame. Foamed resins such as Styrofoam, vacuums, etc. are very efficient as insulating materials but are not used due to strength and volume limitations. Plastics, with low thermal conduction but high strength, are known to be in practical use.
However, there is a need for the back cover and the frame to be good heat conductors, so there is a problem with combining or joining materials having opposing characteristics inside a small case without harming performance.
A back cover similar to that of the past example, but having a newly devised structure and materials, is used as a means to supply body heat from the wrist to the heat receiving portion on the thermoelectric generator in order to solve the above problem.
The back cover supplies heat to the heat receiving portion on the thermoelectric generator, but it is also engaged with the insulating lower frame, a thermal insulator. Heat flows through the insulating lower frame even though it is a thermal insulator. In the past it was common sense to choose a material with good thermal conduction to be used as the back cover material. For the present invention, however, a stainless steel or titanium with an intermediate or lower thermal conductivity is used, making it difficult for heat to flow through the insulating lower frame.
Originally it was not desirable to use a material with a low thermal conduction since the required amount of heat to the heat receiving portion on the thermoelectric generator also dropped. For the present invention, a heat collecting plate formed from a high thermal conductivity material such as copper or aluminum is closely attached or fixedly adhered to the inside base surface of the back cover. The back cover base is an approximately 0.5 mm thin plate, and since it is several millimeters in the radial direction, heat flows predominantly through the thickness of the back cover, towards the heat collecting plate.
According to the present invention, heat from the wrist travels easily to the inside face of the back cover because the back cover thickness is thin, but is not transmitted easily in the radial direction. A heat collecting plate is closely attached to the inside face of the base cover so heat flows from the wrist to the heat collecting plate. The heat collecting plate is made from a material with good thermal conductivity, so the movement of heat occurs quickly. If the heat collecting plate is fixedly adhered to the inside face of the base cover using solder, wax, etc., then even better heat conductivity can be produced.
Further, the cross sectional shape of the heat collecting plate in the present invention is made thick in some parts to store higher temperature heat in the thickened parts. In particular, by thickening the parts in contact with the heat receiving portion on the thermoelectric generator, and enlarging the volume, higher temperature heat is concentrated.
According to the invention of this structure, heat from the wrist, taken in over the entire area of the back cover, is concentrated at the heat collecting plate, just as with a funnel. This brings about an effect like pouring heat into the heat receiving portion on the thermoelectric generator.
In addition, the present invention has a structure where an insulating material is either applied or affixed to the inside face of the heat collecting plate, excluding those portions in contact with the heat receiving portion on the thermoelectric generator in order to retain heat and prevent heat from escaping. It is applied to the inside face of the back cover as well, excluding those portions in contact with water proof packing.
By applying the insulating material, the structure of the present invention prevents a drop in the temperature of the heat collecting plate, and due to the large surface area of the back cover and the heat collecting plate, radiational cooling of the concentrated heat is suppressed, and a higher temperature of heat can be supplied to the thermoelectric generator.
In addition, by inserting a heat transfer cushion between members in the present invention, it is possible to ease the manufacturing precision of the parts, and mass production can be facilitated, while at the same time shock resistance can be increased.